Current trends in the design of electromagnetic machines such as motors have led to compact designs of high efficiency motors. The motor designs have obtained high output power to volume ratios through their use of high magnetic flux density (or "high remanence") magnets on their rotors and high density windings of their stators, increasing efficiency, and through optimized thermal design which increases the motor's ability to dissipate losses.
With the reduction in size of these high efficiency motors the precision with which their components' parts are assembled becomes more important. Specifically, as the size of a motor becomes increasingly smaller, the size and accuracy with which the air gap (which separates the exterior surface of its rotor from the interior surface of its stator) must be similarly reduced in order to compare favorably to a larger model with similar performance characteristics. In addition, with decreasing motor size, the tolerances of the bearings and their associated mounting diameters, rotor shaft and stator bore center axes also decrease, and the slightest misalignment can result in negative effects on motor performance, in increased bearing wear which significantly decreases the operational life of the motor or in contact of the rotating rotor with the stator bore which prevents its proper functioning all together.
Compact high efficiency motors are constructed of basically the same component parts typical to most motors, those being he stator, which is the stationary electromagnetic component of the motor, the rotor, which is the rotating electromagnetic component of the motor, and the endbells, which locate the rotor in relationship to the stator. To achieve the necessary tolerances for the motor's compact size, each of the component parts of the motor must be machined and assembled with high accuracy relative to the other component parts of the motor. The stator must be assembled in the motor housing shell and the motor housing shell must be manufactured to align or register the center axes of the stator bore relative to the housing shell. The endbells are machined with reference to the stator center bore By machining and assembling each of the component parts of the motor with reference to the other component parts of the motor, the center axis of the rotor is closely registered with the center axes of the bearings mounted in the endbells which, in turn, are registered with the center axis of the stator bore when the component parts are assembled in the motor. The precise machining and assembly of the motor component parts is necessary to properly position the rotor in the stator bore and the rotor bearings in the endbell bearing seats. The extremely precise machining and assembly of the motor component parts comprise a major portion of the expense involved in manufacturing compact, high efficiency motors.